Glutathione Deficiency Induces Epigenetic Alterations of Vitamin D Metabolism Genes in the Liver of High-Fat Diet–Induced Type 2 Diabetic Mice

Abstract

Vitamin D (VD) deficiency is an epidemic health problem. Over a billion people worldwide are VD-deficient or insufficient. VD-regulates the functions of over 200 genes and is essential for growth and development. VD-deficiency can result in diabetes, hypertension, heart disease and stroke. VD levels correlate positively with GSH and negatively with insulin resistance in type 2 diabetic patients. HFD-fed mice exhibited elevated blood glucose, and decreased blood GSH and 25(OH)VD with reduced GSH and increased oxidative stress in the liver. We investigated whether GSH deficiency induces epigenetic alterations in VD-metabolism genes in the high-fat diet (HFD) fed mice. The levels of VD-metabolism genes (CYP2R1, CYP27A1, CYP27B1, and VDR) and GSH biosynthesis pathway genes (GCLC, GCLM, GSS, and GSR) were significantly (p<0.005) down-regulated in the liver of HFD-fed mice. Conversely, CYP24A1 which metabolizes the active VD was significantly (p<0.005) increased. In vitro mouse hepatocyte GCLC knockdown decreases GSH and alters VD-regulatory genes in the similar pattern of HFD-fed mice. Further, significant increased DNMTs (1, 3a and 3b) and global DNA methylation levels with decreased TET1 (p<0.005) but not TET2/3 were observed in the cultured hepatocytes and liver. Notably, significant (p<0.005) gene-specific hypermethylation of CYP2R1 (1.71, 2.55; Control vs. HFD), CYP27A1 (7.58, 8.68), CYP27B1 (0.11, 0.77), VDR (0.16, 0.46) and hypomethylation of CYP24A1 (0.59, 0.33) was observed in the liver of HFD-fed (16 weeks) mice compared with control (normal diet) group. GSH deficiency-induced epigenetic alterations (methylation status) of VD-metabolism enzyme genes and the VDR gene appear to play a significant role in the circulating VD. These findings indicate that GSH epigenetically regulates VD-metabolism genes in obesity/T2DM and a novel adjuvant therapeutic target for restoring VD-deficiency in susceptible populations. Disclosure R. Parsanathan: None. S.K. Jain: None.